1. Field of the Invention
The present invention relates to an image forming apparatus and method, and more particularly, to an image forming apparatus and method for forming images on a recording medium by using a radiation-curable ink which is cured by irradiation of radiation such as ultraviolet light or the like.
2. Description of the Related Art
Technology using ultraviolet-curable ink (so-called UV ink) in an inkjet type image forming apparatus is known. Japanese Patent Application Publication No. 2004-42548 discloses technology for preventing the occurrence of mottling and bleeding, in cases where dots are recorded by depositing droplets of ultraviolet-curable ink from different nozzles, at prescribed staggered time intervals, by irradiating ultraviolet light in conjunction with the deposition timing of the respective droplets, thereby pre-curing mutually adjacent droplets to a degree which prevents them from mixing together, and then subsequently irradiating ultraviolet light again to perform main curing.
However, in ultraviolet-curable inks, it is rare for the viscosity to pass through a semi-solidified state and for the ink to then solidify, due to irradiation of radiation, and in most cases, the ink changes directly from a liquid state to a solid state. In other words, when ultraviolet light is irradiated onto ultraviolet-curable ink droplet after the ink droplet has been deposited, rather than the viscosity of the ink droplet increasing and the ink droplet thereby solidifying in a continuous fashion as the ultraviolet light is irradiated, the solidification takes place in a step fashion (liquid phase to solid phase) from the outer surface of the approximately hemispherical ink droplet toward the inside.
In order to deposit ink droplets at high speed while preventing landing interference therebetween, it is necessary to deposit one droplet so as to overlap with another droplet at a timing at which landing interference will not occur, during the curing process which progresses from the surface of the ink droplet to the inner side thereof. However, this timing varies with different conditions. In Japanese Patent Application Publication No. 2004-42548, there is no disclosure regarding optimal droplet deposition timing which takes account of the aforementioned point, and it is not possible to achieve both high-speed printing and high-quality printing.